Evaporation apparatus, organic material evaporation source, and method of manufacturing thin organic film

ABSTRACT

An inactive gas is introduced into an organic material evaporation source to place a thin organic film material in the organic material evaporation source in an atmosphere having a relatively high pressure, and the temperature of the thin organic film material is increased up to a certain temperature. Then, the organic material evaporation source is evacuated to lower the pressure around the thin organic film material for thereby causing the thin organic film material to emit a vapor. Since no wasteful vapor is emitted from the thin organic film material, the thin organic film material is effectively utilized. Because the inactive gas acts as a heating medium, the temperature of the thin organic film material is increased at a high rate, and the thin organic film material is uniformly heated. When the temperature of the thin organic film material is lowered in an inactive gas atmosphere, it can be lowered at a high rate. The inactive gas is introduced directly into the organic material evaporation source by an on-off valve, the time required to evacuate the organic material evaporation source is reduced. A liquid thin organic film material may be heated by a heating medium in the organic material evaporation source, so that the liquid thin organic film material will not be heated to a temperature higher than the temperature of the heating medium, and hence will not suffer bumping due to a temperature overshooting.

This application is a divisional application of prior application Ser.No. 09/478,911 filed Jan. 7, 2000, which in turn is a divisionalapplication of prior application Ser. No. 09/088,088 filed Jun. 1, 1998now U.S. Pat. No. 6,101,316.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an evaporation apparatus for forming athin organic film on an object, an organic material evaporation sourcefor use in such an evaporation apparatus, and a method of manufacturinga thin organic film.

2. Description of the Related Art

The conventional electronic material technology has primarily focused oninorganic materials including semiconductors. However, recent years haveseen more attention drawn to functional thin organic films of organiccompounds as electronic materials.

Organic compounds are advantageous for use as electronic materialsbecause they provide more diverse reactions and properties thaninorganic materials and can be surface-treated with lower energy thaninorganic materials.

Functional thin organic films are used in organic electroluminescencedevices, piezoelectric sensors, pyroelectric sensors, electricinsulating films, etc. Electroluminescence devices can be used asdisplay panels, and efforts are being made to develop a techniquecapable of forming a thin organic film uniformly on a large substratefor producing an electroluminescence display device with a large displayarea.

Conventional thin organic film fabrication processes employ vacuumevaporation apparatus primarily designed for forming thin metal filmsincluding thin films of Al and SiO2, and thin organic films. Evaporationapparatus designed for the fabrication of thin organic films have notyet been developed in the art.

Thin organic film materials have features of their own in contrast tothin inorganic film materials as described below.

Thin organic film materials have high vapor pressures. While metalevaporation sources have an evaporation temperature ranging from 600° C.to 2000° C., thin organic film materials have a lower evaporationtemperature ranging from 0° C. (often sub-zero temperatures) to 400° C.Many thin organic film materials tend to be decomposed in a temperaturerange from 20° C. to 400° C. Therefore, it is preferable to effectprecise temperature control for evaporating thin organic film materials.

When a thin metal film is to be fabricated, an electron beam evaporationapparatus is used to apply an electron beam to a metal evaporationsource. However, if an electron beam is applied to a thin organic filmmaterial, the thin organic film material will be decomposed because theenergy of the electron beam is too high for the thin organic filmmaterial.

Some thin organic film materials are powdery in nature. Generally,powdery materials have poor thermal conductivity. When a powderymaterial is heated in a vacuum, its temperature cannot easily be raisedor lowered due to the heat insulating effect of the vacuum, and theactual temperature of the powdery material may be delayed with respectto a target temperature at which the powdery material is to becontrolled.

Once the temperature of a powdery evaporation source is raised, thepowdery evaporation source cannot quickly be cooled by radiation only.Therefore, the material evaporation from the powdery evaporation sourceis not finished immediately when the heating of the powdery evaporationsource is stopped. The material evaporation cannot thus be controlledsharply.

Inasmuch as thin organic film materials have high vapor pressures,absorbs on the wall of a vacuum chamber at a low temperature are likelyto be released (reevaporated) as the temperature of the vacuum chamberrises. If such released particles find their way into a thin organicfilm formed on an object, then they tend to degrade characteristics ofthe thin organic film.

Many thin organic film materials are capable of easily absorbingmoisture. Some of them have their properties modified when they absorbmoisture. If moisture is trapped into a multilayer thin organic film asit is formed, then properties of the interlayer boundaries are modified.Such property modifications are liable to result in defects in the finalperformance of functional devices including electroluminescence devices,piezoelectric sensors, and pyroelectric sensors.

Metal evaporation sources exhibits directivity upon evaporation. Themovement of vapor from metal evaporation sources is substantiallystraight therefrom according to the cosine law. The movement of somethin organic film materials vapor, however, is curved like the directionof particle motion due to diffusion.

For forming an evaporated polymeric film, it is necessary that thecomposition ratio of two thin organic film materials to be evaporated atthe same time be in accordance with a stoichiometric ratio. If thecomposition ratio differs from a stoichiometric ratio, then a fabricatedpiezoelectric or pyroelectric device, for example, will lose itsfunctions or suffer function degradation. Film growth speeds need to beprecisely controlled for equalizing composition ratio to astoichiometric ratio.

As described above, thin organic film materials have many propertieswhich make themselves difficult to handle with ease.

FIGS. 8A through 8E of the accompanying drawings show variousconventional evaporation sources. These illustrated evaporation sources,however, are not suitable for use with thin organic film materialsbecause of the above properties of thin organic film materials anddemanded properties of thin organic films.

FIG. 8A shows a direct resistance heating evaporation source includingan evaporation source container 101 of metal which is heated by anelectric current passing directly therethrough for evaporating a thinfilm material.

The direct resistance heating evaporation source provides excellenttemperature stability in a temperature range in which metals are melted.However, it has poor temperature stability and controllability in atemperature range in which thin organic film materials are evaporated,with the result that an organic compound vapor (the vapor of a thinorganic film material) will be produced at an unstable rate.

Some thin organic film materials have an ability to corrode or reactwith metals. Those thin organic film materials cannot be used with theevaporation source container 101 which is made of metal.

FIG. 8B shows a conical-basket evaporation source having an evaporationsource container 111 and a resistance heater 112 disposed around theevaporation source container 111. When the resistance heater 112 isenergized, it indirectly heats a thin film material in the evaporationsource container 111 to evaporate the thin film material.

FIG. 8C shows a Knudsen-cell evaporation source having an evaporationsource container 121 and a resistance heater 122 disposed around theevaporation source container 121. When the resistance heater 122 isenergized, it indirectly heats a thin film material in the evaporationsource container 121 to evaporate the thin film material.

Each of the evaporation sources shown in FIGS. 8B and 8C providesexcellent temperature stability in a temperature range in which metalsare melted. However, it has poor temperature stability andcontrollability in a temperature range in which thin organic filmmaterials produce vapor, with the result that an organic compound vapor(the vapor of a thin organic film material) will be produced at anunstable rate.

The resistance heater 112 usually comprises a bare metal wire. Themovement of thin organic film materials vapor is more likely to becurved than that of thin inorganic film materials. If a thin organicfilm material contains a metal chelate or the like, it may develop ashort circuit between turns of the resistance heater 112.

Because the Knudsen-cell evaporation source is of a complex structure,it cannot easily be cleaned, and the thin film material cannot fully beremoved from the Knudsen-cell evaporation source after an evaporationprocess. Therefore, when the thin film material in the evaporationsource container 121 is replaced with another thin film material, thenew thin film material may possibly be contaminated with a residue ofthe previous thin film material.

FIG. 8D shows a lamp-heater type evaporation source comprising anevaporation source container 131 made of a light-transmissive materialsuch as quartz and an infrared lamp 133 disposed above the evaporationsource container 131. The infrared lamp 133 applies radiant heat to theevaporation source container 131 to evaporate a thin film material inthe evaporation source container 131.

The lamp-heater-type evaporation source has excellent temperaturecontrollability at low temperatures. However, since the evaporationsource container 131 has a large specific heat capacity, there tends tobe developed a difference between the a target temperature at which thethin film material is to be controlled and an actual temperature of thethin film material. If the temperature of the thin film material ismeasured for being controlled, a temperature overshooting tends tooccur, decomposing a thin organic film material placed in theevaporation source container 131.

The evaporation source container 131 needs to be made of a transparentmaterial such as quartz or the like in order to allow radiant heatemitted from the infrared lamp 133. However, the transparent material isapt to be damaged when it is cleaned or replaced.

After the evaporation source container 131 has been used for a longperiod of time, it is irregularly fogged and transmits differentinfrared intensities at different positions. Such different infraredintensities cause a thin organic film material, which has poor thermalconductivity, placed in the evaporation source container 131 to beoverheated locally.

Some thin organic film materials are modified by light at a certainwavelength. Such thin organic film materials cannot be evaporated by thelamp-heater evaporation source shown in FIG. 8D.

FIG. 8E shows an electron beam gun evaporation source which applies anelectron beam 145 to a thin film material to evaporate the thin filmmaterial. The electron beam gun evaporation source shown in FIG. 8E,however, cannot be used to evaporate thin organic film materials becausethe electron beam 145 decomposes thin organic film materials whenapplied to them.

As described above, the conventional evaporation sources shown in FIGS.8A through 8E will suffer various problems if applied to the evaporationof thin organic film materials. Particularly, the decomposition of thinorganic film materials due to a temperature overshooting and thedifficulty in heating thin organic film materials are problems that havenot been experienced with thin inorganic film materials, and should bealleviated.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide anevaporation apparatus which is capable of increasing the temperature ofan organic film material in a short period of time up to a desiredtemperature without causing a temperature overshooting and thermallydecomposing main constituents of the organic film material.

Another object of the present invention is to provide an evaporationapparatus which is capable of preventing an organic film material fromproducing a vapor except when the organic film material is evaporated,for thereby effectively exploiting the organic film material from.

Still another object of the present invention is to provide an organicmaterial evaporation source which can uniformly heat a liquid organicfilm material up to a constant temperature, and allows such a liquidorganic film material to be handled with ease.

Yet still another object of the present invention is to provide a methodof manufacturing an organic film with such an evaporation apparatus oran organic material evaporation source.

According to the present invention, there is provided an evaporationapparatus comprising a vacuum chamber for holding therein an object onwhich an organic film is to be formed, an evacuating system connected tothe vacuum chamber, for evacuating the vacuum chamber, an organicmaterial evaporation source disposed in the vacuum chamber, forcontaining an organic film material, and having temperature controlmeans for controlling the temperature of the organic film material toevaporate the organic film material for forming an organic film on theobject held in the vacuum chamber, and a gas supply system connected tothe vacuum chamber, for introducing an inactive gas into the vacuumchamber.

After the vacuum chamber is evacuated, an inactive gas is introducedinto the vacuum chamber to place the organic film material in theorganic material evaporation source in an inactive gas atmosphere. Whenthe temperature of the organic film material is controlled, the inactivegas produces a convective flow around the organic film material, withthe result that the rate at which the temperature of the organic filmmaterial is increased or reduced is higher than if the organic filmmaterial were placed in a vacuum atmosphere. If the organic filmmaterial is powdery, the inactive gas enters between particles of thepowdery organic film material and acts as a heating medium, increasingthe heat transfer coefficient between the particles of the powderyorganic film material. Therefore, the temperature controllability of theorganic film material is increased, preventing the organic film materialfrom suffering localized overheating and a temperature overshooting, sothat the organic film material is prevented from being decomposed.

An organic material evaporation source according to the presentinvention comprises a container for containing a organic film materialtherein, an outlet port, and an on-off valve connected between thecontainer and the outlet port, the on-off valve being openable forconnecting an interior atmosphere in the container to an exterioratmosphere outside of the container through the outlet port, andclosable for disconnecting the interior atmosphere in the container fromthe exterior atmosphere outside of the container.

After an inactive gas is introduced into a vacuum chamber connected tothe organic material evaporation source, the on-off valve is closed toplace the organic film material in an inactive gas atmosphere.

Generally, an organic compound emits a less vapor in an inactive gasatmosphere than in a vacuum atmosphere. Therefore, when the organic filmmaterial is heated and cooled in the inactive gas atmosphere, theemission of a vapor from the organic film material is suppressed duringthat time. Accordingly, any wasteful vapor that would not contribute tothe formation of an organic film is not emitted from the organic filmmaterial. The organic film material is thus effectively utilized, andthe cost of a manufactured organic film is lowered.

When the organic film material is heated to a temperature at which itwould be evaporated in the vacuum atmosphere, the organic film materialmay be prevented from being evaporated in the inactive gas atmospheredepending on the pressure of the inactive gas atmosphere. Therefore,when the vacuum chamber is evacuated after the temperature of theorganic film material is increased in the inactive gas atmosphere, anorganic film can be formed without the emission of a wasteful vapor fromthe organic film material.

The organic material evaporation source further comprises a gas supplysystem connected to the container, for selectively introducing a gasinto the container while the on-off valve is being closed. The organicfilm material can thus be placed in an inactive atmosphere while thevacuum atmosphere is being developed in the vacuum chamber.

It is therefore not necessary to introduce an inactive gas into thevacuum chamber which is of a large volume in order to suppress theemission of a vapor from the organic film material.

The organic material evaporation source further comprises an evacuatingsystem connected to the container, for selectively evacuating thecontainer while the on-off valve is being closed. The on-off valve canbe opened after the container is evacuated to discharge the gas. Theorganic material evaporation source further comprises a gas supplysystem connected to the container, for selectively introducing a gasinto the container while the on-off valve is being closed.

The organic film material tends to be separated from the vapor when itis cooled. The organic material evaporation source preferably furthercomprises heating means disposed between the container and the outletport across the on-off valve, for heating a passage from the containerto the outlet port across the on-off valve. The heating means serves toprevent a vapor emitted from the organic film from being cooled untilthe vapor is discharged from the outlet port into the vacuum chamber.

According to the present invention, an organic material evaporationsource comprises a container for containing a liquid organic filmmaterial therein, and a heating medium circulatory path for passing aheating medium therethrough, the heating medium circulatory path beingdisposed around the container. Since the container can be heated orcooled uniformly by the heating medium, the ability for the liquidorganic film material to be uniformly heated is increased.

The organic material evaporation source further comprises a heatingmedium source for controlling the temperature of the heating medium toheat or cool the liquid organic film material contained in thecontainer. Because of a heat exchange between the liquid organic filmmaterial and the heating medium, it is possible to increase or reducethe temperature of the liquid organic film material with accuracy. Whenthe temperature of the liquid organic film material is to be increased,since it will not be higher than the temperature of the heating medium,the liquid organic film material is prevented from being locallyoverheated.

As the liquid organic film material is not heated by heat radiation, itsheating will not be made irregular by frosted regions of the container.Because the container is not required to be transparent, it may be madeof a ceramic material having a high heat transfer coefficient, and hencecan be handled with ease.

The organic material evaporation source further comprises a casingdisposed around the container, the heating medium circulatory path beingdefined between the container and the casing. Inasmuch as a heatexchange occurs between the organic film material and the heating mediumthrough the wall of the container, the efficiency of the heat exchangeis high, resulting in increased temperature controllability.

The organic material evaporation source further comprises a heatinsulating member disposed around the casing for higher thermalefficiency and temperature controllability.

Alternatively, the organic material evaporation source further comprisesa casing disposed around the container, the heating medium circulatorypath being defined between the container and the casing, and a heatingmedium source for controlling the temperature of the heating medium toheat or cool the liquid organic film material contained in thecontainer.

As described above, the rate at which a vapor is emitted from an organicfilm material varies depending on the pressure of an atmosphere aroundthe organic film material. According to the present invention, there isalso provided a method of manufacturing an organic film by emitting avapor from an organic film material placed in an organic materialevaporation source to form an organic film on an object, comprising thestep of controlling the pressure of an atmosphere around the organicfilm material to control the rate at which the vapor is emitted from theorganic film material.

According to the present invention, there is further provided a methodof manufacturing an organic film by emitting a vapor from an organicfilm material placed in an organic material evaporation source to forman organic film on an object, comprising the steps of increasing thepressure of an atmosphere around the organic film material to suppressthe emission of the vapor from the organic film material when thetemperature of the organic film material is increased, and thereafter,reducing the pressure of the atmosphere around the organic film materialto start emitting the vapor from the organic film material.

When the pressure of the atmosphere is increased at the time thetemperature of the organic film material is increased, the temperatureuniformity of the organic film material is increased, shortening thetime required to heat the organic film material to increase itstemperature up to a desired temperature. When the pressure of theatmosphere is then reduced, the organic film material immediately startsemitting a vapor. Consequently, the time required to form an organicfilm from the vapor of the organic film material is reduced.

As described above, the organic film material can start and stopemitting a vapor simply by controlling the degree of vacuum of theatmosphere around the organic film material after the temperature of theorganic film material is increased. Therefore, any wasteful emission ofthe vapor of the organic film material which is expensive is prevented.

The step of increasing the pressure of the atmosphere around the organicfilm material comprises the step of introducing an inactive gas into theatmosphere around the organic film material. The pressure of theatmosphere may be reduced by evacuating the gas.

The method further comprises the step of increasing the pressure of theatmosphere around the organic film material to stop emitting the vaporfrom the organic film material.

Since the emission of the vapor is immediately stopped, the evaporationof the organic film material can be controlled sharply, and any wastefulemission of the vapor of the organic film material which is expensive isprevented. For cooling the organic film material after an organic filmhas been formed, the organic film material may be placed in anatmosphere having a high pressure to increase the rate at which theorganic film material is cooled.

Experiments have confirmed that when an organic film material is heatedto a temperature at which it emits a vapor in a low-pressure atmosphere,the organic film material does not emit a vapor if the pressure of theatmosphere around the organic film material is increased to a range from13.3 Pa (0.1 Torr) to 2.0×10³ Pa (15.0 Torr) depending on the type ofthe organic film material.

If the pressure of the atmosphere were too high, the amount of aninactive gas used would be increased, and the time required to evacuatethe inactive gas to lower its pressure would also increased. Therefore,it is preferable to set the pressure to 66.5 Pa (0.5 Torr) forsuppressing the emission of a vapor.

After the temperature of the organic film material is increase in such ahigh-pressure atmosphere, the inactive gas is evacuated to develop alow-pressure atmosphere to allow the organic film material to emit avapor. For increasing the quality of an organic film to be formed, it ispreferable to lower the pressure of the atmosphere to 1.33×10⁻⁴ Pa(1.0×10⁻⁶ Torr) or less, or more preferably to 1.33×10⁻⁵ Pa (1.0×10⁻⁷Torr) or less.

The method further comprises the steps of, before the temperature of theorganic film material is increased, reducing the pressure of theatmosphere around the organic film material and increasing thetemperature of the organic film material to degas the organic filmmaterial. To degas the organic film material, it is preferable to heatthe organic film material to a temperature lower than its evaporationtemperature.

A method according to claim 13, wherein said step of increasing thepressure of the atmosphere around said organic film material comprisesthe step of introducing an inactive gas into the atmosphere around saidorganic film material.

A method according to claim 13, wherein said step of increasing thepressure of the atmosphere around said organic film material comprisesthe step of introducing an inactive gas into the atmosphere around saidorganic film material; and

comprising the step of reducing the temperature of said organic filmmaterial.

The above and other objects, features, and advantages of the presentinvention will become apparent from the following description when takenin conjunction with the accompanying drawings which illustrate preferredembodiments of the present invention by way of example.

BRIEF DESCRIPTION OF THE-DRAWINGS

FIG. 1 is a schematic cross-sectional view of an evaporation apparatusaccording to an embodiment of the present invention;

FIG. 2 is a schematic cross-sectional view of an organic materialevaporation source used in the evaporation apparatus shown in FIG. 1;

FIG. 3 is a schematic cross-sectional view of an organic materialevaporation source according to another embodiment of the presentinvention;

FIG. 4 is a flowchart of a sequence of a method of manufacturing a thinorganic film according to the present invention;

FIG. 5 is a graph showing the manner in which the temperature of a thinorganic film material and the evaporation rate thereof vary with timewhen a thin organic film is formed by the method according to thepresent invention;

FIG. 6 is a graph showing the relationship between the temperature andevaporation ratio of Alq₃ and TPD;

FIG. 7 is a graph showing the manner in which the temperature of a thinorganic film material and the evaporation rate thereof vary with timewhen a thin organic film is formed by a conventional method; and

FIGS. 8A through 8E are views showing conventional evaporation sources.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1, an evaporation apparatus 10 according to anembodiment of the present invention has a vacuum chamber 11 to whichthere are connected a gas supply system 18 and an evacuating system 19.The evacuating system 19 has a vacuum pump 21 which evacuates the vacuumchamber 11 to a high vacuum when it actuates.

The vacuum chamber 11 has a plurality of organic material evaporationsources disposed on a bottom wall thereof. In FIG. 1, the organicmaterial evaporation sources include two organic material evaporationsources 12 ₁, 12 ₂. The organic material evaporation sources 12 ₁, 12 ₂have respective discharge ports 14 ₁, 14 ₂. When thin organic filmmaterials are placed in the respective organic material evaporationsources 12 ₁, 12 ₂ and heated to predetermined temperatures, the thinorganic film materials emit vapors of organic compounds, which aredischarged (desorbed) through the discharge ports 14 ₁, 14 ₂ into thevacuum chamber 11.

The vacuum chamber 11 houses therein a substrate holder 30 disposedupwardly of the organic material evaporation sources 12 ₁, 12 ₂. Thesubstrate holder 30 holds on its lower surface an object 13, i.e., aglass substrate 13, such that a surface of the glass substrate 13 onwhich a thin organic film is to be deposited faces the discharge ports14 ₁, 14 ₂.

The gas supply system 18 comprises a gas pipe 28, a mass flow controller23, a gas container 22, and two valves 24 ₁, 24 ₂. The gas pipe 28 has agas inlet port 29 opening into the vacuum chamber 11. The gas container22 is connected through the valve 24 ₁, the mass flow controller 23, thevalve 24 ₂, and the gas pipe 28 to the interior atmosphere of the vacuumchamber 11.

The gas container 22 is filled with an inactive gas such as a nitrogengas, an argon gas, or the like. It is assumed in this embodiment thatthe gas container 22 is filled with a nitrogen gas. When the valves 24₁, 24 ₂ are opened, the nitrogen gas is introduced at a rate controlledby the mass flow controller 23 into the vacuum chamber 11 through thegas inlet port 29.

The vacuum chamber 11 also houses therein a substrate shutter 35 whichcan be selectively opened and closed near the surface of the glasssubstrate 13, and a pair of evaporation source shutters 33 ₁, 33 ₂,which can be selectively opened and closed near the surface of therespective discharge ports 14 ₁, 14 ₂ of the organic materialevaporation sources 12 ₁, 12 ₂. When the substrate shutter 35 and theevaporation source shutters 33 ₁, 33 ₂ are closed, organic compoundvapors which are discharged from the discharge ports 14 ₁, 14 ₂ into thevacuum chamber 11 are prevented from reaching the surface of the glasssubstrate 13, and hence no thin organic film grows on the glasssubstrate 13.

Film thickness monitors 36 ₁, 36 ₂ are disposed above the evaporationsource shutters 33 ₁, 33 ₂, respectively, in positions which do notinterfere with organic compound vapors that travel from the dischargeports 14 ₁, 14 ₂ toward the glass substrate 13. When the evaporationsource shutters 33 ₁, 33 ₂ are opened, organic compound vaporsdischarged from the discharge ports 14 ₁, 14 ₂ are deposited to the filmthickness monitors 36 ₁, 36 ₂, which then measure the rate at which athin organic film is deposited on the surface of the glass substrate 13.

In the vacuum container 11, there are also disposed cooling panels 31,32, which are hermetically supplied with liquid nitrogen, around theglass substrate 13 and on the bottom wall of the vacuum container 11.When liquid nitrogen is introduced into the cooling panels 31, 32 afterthe vacuum chamber 11 has been evacuated, the cooling panels 31, 32efficiently attract water molecules present in the vacuum chamber 11 forthereby removing water molecules from the interior atmosphere of thevacuum chamber 11.

If the cooling panels 31, 32 did not exist, then organic compound vaporsattracted to wall surfaces of the vacuum chamber 11 would be releasedand a thin organic film deposited on the surface of the glass substrate13 would be contaminated by the released vapor. The cooling panels 31,32 are effective to trap organic compound vapors directed toward wallsurfaces of the vacuum chamber 11 and prevent the trapped organiccompound vapors from being released. Therefore, the cooling panels 31,32 allow a high-quality thin organic film to be deposited on the surfaceof the glass substrate 13.

The substrate holder 30 has a coiled pipe 37 for passing a heatingmedium therethrough. When a temperature-controlled heating medium flowsthrough the coiled pipe 37, it heats the glass substrate 13 with goodtemperature controllability to a temperature ranging from 50° C. to 100°C. while a thin organic film is being deposited on the surface of theglass substrate 13. Since the glass substrate 13 is controlled intemperature, a thin organic film is deposited with good adhesion on theglass substrate 13.

As shown in FIG. 2, each of the organic material evaporation sources 12₁, 12 ₂ is hermetically mounted on the bottom wall of the vacuum chamber11 by an O-ring 58 and a flange 59. Each of the organic materialevaporation sources 12 ₁, 12 ₂ has a casing 51 including an upperopening toward the vacuum chamber defined therein which serves as one ofthe discharge ports 14 ₁, 14 ₂.

The casing 51 houses therein a container 50 for supplying a thin organicfilm material 54 and a bottomed cylindrical soaking tube 55 disposedaround the container 50. A microheater 52 is coiled around the soakingtube 55. The microheater 52 comprises a thin pipe of stainless steelfilled with an inorganic insulating material and a resistive heatingelement such as a nichrome wire placed in the thin pipe.

A thermocouple 56 is mounted on an outer surface of the lower end of thesoaking tube 55. When the microheater 52 is energized by a power supplypositioned outside of the vacuum chamber 11 while the temperature of thesoaking tube 55 is being kept at a predetermined level by thethermocouple 56, the thin organic film material 54 placed in thecontainer 50 is maintained at a desired temperature in the range from150° C. to 400° C.

A reflector 53 is disposed around the microheater 52 for reflectingradiant heat directed from the microheater 52 toward the casing 51 forthereby efficiently heating the container 50 while minimizing anincrease in the temperature of the casing 51.

The microheater 52 has turns which are progressively dense toward thedischarge ports 14 ₁, 14 ₂ and progressively less dense toward the lowerclosed end of the container 50, so that the temperature of the dischargeports 14 ₁, 14 ₂ will be higher than those of the container 50 and thethin organic film material 54 placed in the container 50. As a result, aorganic compound vapor emitted from the thin organic film material 54will not be deposited on surfaces near the discharge ports 14 ₁, 14 ₂.

A method of manufacturing a thin organic film according to an embodimentof the present invention, using the evaporation apparatus 10 shown inFIGS. 1 and 2, will be described below with reference to FIG. 4.

Alq₃ [Tris(8-hydroxyquinoline)aluminum, sublimed] expressed by thefollowing chemical formula:

is placed as a thin organic film material in one of the organic materialevaporation sources 12 ₁, 12 ₂. The Alq₃ is a powdery sublimable thinorganic film material.

The vacuum pump 21 is actuated to develop a vacuum atmosphere in thevacuum chamber 11, and the glass substrate 13 is introduced into thevacuum chamber 11. The vacuum chamber 11 is further evacuated to placethe Alq₃ in the organic material evaporation source 12 ₁ and the glasssubstrate 13 in a vacuum atmosphere having a pressure of 1.0×10⁻⁶ Torrin STEP S1 (see FIG. 4).

Then, the microheater 52 in the organic material evaporation source 12 ₁is energized to heat the Alq₃ to a temperature ranging from 100° C. to200° C. At this temperature, the amount of a vapor emitted from the Alq₃is small, but an adsorbed gas is discharged.

The Alq₃ is degassed for a period of time ranging from 20 minutes to 30minutes in STEP S2, after which a nitrogen gas is introduced as aninactive gas from the gas inlet port 29 into the vacuum chamber 11 inSTEP S3 while the vacuum chamber 11 is being evacuated.

When the vacuum chamber 11 and the organic material evaporation source12 ₁ are filled with an inactive gas atmosphere having a pressure of13.3 Pa (0.1 Torr), the current supplied to the microheater 52 isincreased to increase the temperature of the Alq₃ in the organicmaterial evaporation source 12 ₁ to an evaporating temperature (about300° C. for the Alq₃) in STEP S4. As the temperature rises, since theAlq₃ is placed in the inactive gas atmosphere, the heat is efficientlytransferred between particles of the Alq₃. Therefore, no temperatureovershooting occurs, and no vapor of the Alq₃ is observed.

When the Alq₃ is stabilized at its evaporating temperature, the ingressof the inactive gas is stopped, and the vacuum chamber 11 is evacuatedagain to a vacuum atmosphere having a pressure of 1.33×10⁻⁴ Pa (1.0×10⁻⁶Torr) in STEP S5.

When the Alq₃ is stabilized under the vacuum pressure, the evaporationsource shutter 33 ₁ is opened while the substrate shutter 35 is beingclosed, discharging an Alq₃ vapor from the discharge port 14 ₁.

The Alq₃ vapor reaches the film thickness monitor 36 ₁, forming a thinorganic film on its surface. The rate of growth of the thin organic filmis measured. When the measured rate of growth is stabilized, thesubstrate shutter 35 is opened, starting to form a thin organic film ofAlq₃ on the surface of the glass substrate 13 in STEP S6.

The thin organic film of Alq₃ is formed on the surface of the glasssubstrate 13 for 5 minutes. When the thickness of the thin organic filmof Alq₃ on the surface of the glass substrate 13 has reached apredetermined value, the substrate shutter 35 and the evaporation sourceshutter 33 ₁ are closed, and the microheater 52 is de-energized, thuscompleting the evaporation process in STEP S7.

Thereafter, an inactive gas is introduced from the gas inlet port 29into the vacuum chamber 11 to place the Alq₃ in the organic materialevaporation source 12 ₁ in an inactive gas atmosphere having a pressureof 13.3 Pa (0.1 Torr), thereby stopping the evaporation of the Alq₃. inSTEP S8. Since the inactive gas acts as a heating medium and aconvective flow is produced, the Alq₃ is cooled quickly in STEP S9.

FIG. 5 shows the manner in which the temperature of the Alq₃ and theevaporation rate thereof vary after the temperature of the Alq₃ startsincreasing in the inactive gas atmosphere until the evaporation processis finished and the Alq₃ is cooled. FIG. 6 shows the relationshipbetween the temperature and evaporation ratio of the Alq₃ in the vacuumatmosphere and TPD represented by the following chemical formula:

It can be seen from FIG. 6 that Alq₃ emits a thin organic film materialvapor at a temperature of about 300° C. and TPD emits a thin organicfilm material vapor at a temperature of about 230° C. A study of FIG. 5shows that no Alq₃ vapor is produced in the inactive gas atmosphere evenwhen it is heated to a temperature at which a thin organic film materialvapor is produced in the vacuum atmosphere. Therefore, it can beunderstood that the production of a thin organic film material vapor canbe controlled by the pressure of the inactive gas atmosphere.

It can be found from FIG. 5 that when the temperature of a thin organicfilm material is increased in the inactive gas atmosphere, notemperature overshooting is observed.

FIG. 7 shows the manner in which the temperature of Alq₃ and theevaporation rate thereof vary with time when a thin organic film isformed by a conventional method, i.e., not using an inactive gas. It canbe seen from FIG. 7 that since the Alq₃ is thermally insulated in thevacuum when its temperature is increased, it is partially overheated,resulting a temperature overshooting. When the temperature of the Alq₃is increased and reduced, an Alq₃ vapor which does not contribute to theformation of a thin organic film is produced in a large amount.

FIG. 3 shows an organic material evaporation source 42 according toanother embodiment of the present invention, which is suitable forheating and cooling a thin organic film material in the form of aliquid.

As shown in FIG. 3, the organic material evaporation source 42 is of theoil-bath type for controlling the temperature of a thin organic filmmaterial, i.e. , heating and cooling a thin organic film material, witha liquid heating medium. The organic material evaporation source 42 maybe used in place of the organic material evaporation sources 12 ₁, 12 ₂in the evaporation apparatus 10 shown in FIG. 1.

The organic material evaporation source 42 is particularly suitable forkeeping a thin organic film material at a constant temperature in thetemperature range from −20° C. to 180° C. for thereby evaporating thethin organic film material. The organic material evaporation source 42generally comprises a casing 71, a container 70, and a heating mediumsource 60.

The container 70 is disposed in the casing 71, jointly making up adouble-walled structure having a heating medium circulatory path 78defined between the container 70 and the casing 71. The casing 71 issurrounded by a heat insulating member 80. The heating medium source 60comprises an oil bath 63, a heater 65, and an immersed cooler 64. Theoil bath 63 contains a heating medium 61 which comprises silicone oilthat can be heated by the heater 65 or cooled by the immersed cooler 64.

A supply pipe 66 ₁ has a tip end placed in the heating medium 61, and acirculation pump 62 is connected in the supply pipe 66 ₁. When thecirculation pump 62 is actuated, it draws the heating medium 61 from theoil bath 63, and supplies the heating medium 61 through the supply pipe66 ₁ into the heating medium circulatory path 78. After a heat exchangeis carried out between the heating medium 61 and a thin organic filmmaterial 74 in the container 70, the heating medium 61 is dischargedfrom the heating medium circulatory path 78 through a discharge pipe 66₂, and flows back to the oil bath 63.

The container 70 has an upper end hermetically joined to a lower end ofa vapor outlet pipe 75, which has an outlet port 44 in its upper endthat is open into a vacuum chamber (not shown in FIG. 3). A thin organicfilm material vapor produced from the thin organic film material 74 inthe container 70 flows through the vapor outlet pipe 75 and isdischarged through the outlet port 44 into the vacuum chamber.

The vapor outlet pipe 75 has an on-off valve 45 for controlling thepassage of a gas therethrough. To the vapor outlet pipe 75 between theon-off valve 45 and the container 70, there is connected an end of a gaspipe 43 whose opposite end is connected to a gas container 46 filledwith an inactive gas such as a nitrogen gas, an argon gas, or the like.The gas pipe 43 has a pair of gas valves 48 ₁, 48 ₂. The gas pipe 43 isbranched between the gas valves 48 ₁, 48 ₂ into a branch pipe that has agas valve 48 ₃ and is connected to a vacuum pump 47.

The thin organic film material 74 contained in the container 70comprises a liquid thin organic film material such asMDA(4,4′-diaminodiphenylmethane) represented by the following chemicalformula:

or MDI(4,4′-diphenylmethane diisocyanate) represented by the followingchemical formula:

The organic material evaporation source 42 operates as follows:

The on-off valve 45 and the gas valve 48 ₂ connected to the gascontainer 46 are closed, and the vacuum pump 47 is actuated. When thegas valves 48 ₁, 48 ₃ are opened, the container 70 is evacuated to placethe thin organic film material 74 in a vacuum atmosphere.

The circulation pump 62 is actuated to heat the thin organic filmmaterial 74 up to a temperature at which no thin organic film materialvapor is produced in the vacuum atmosphere. The thin organic filmmaterial 74 is thus degassed.

Then, the gas valve 48 ₃ is closed, and the gas valve 48 ₂ is opened,introducing the inactive gas from the gas container 46 through the gaspipe 43 into the container 70, thus placing the thin organic filmmaterial 74 in an inactive gas atmosphere.

After an inactive gas atmosphere having a pressure ranging from 1.33 Pato 2.0×10³ Pa(0.1 to 15.0 Torr) is developed in the container 70, thegas valves 48 ₁, 48 ₂ are closed, and the heating medium 61 is heated bythe heater 65 and introduced into the heating medium circulatory path78. In the heating medium circulatory path 78, the heating medium 61flows while in contact with the outer circumferential and bottomsurfaces of the container 70 for uniformly heating the container 70 andhence the thin organic film material 74 contained therein.

When the temperature of the heating medium 61 is increased at apredetermined rate, the temperature of the thin organic film material 74is also increased at a corresponding rate.

Since the thin organic film material 74 is placed in the inactive gasatmosphere having the above pressure, the thin organic film material 74is not evaporated even when heated to a temperature at which it wouldotherwise be evaporated under a lower pressure (in a vacuum atmosphere).

When the thin organic film material 74 is stabilized at its evaporationtemperature, the valves 48 ₁, 48 ₃ are opened, with the valve 48 ₂remaining closed, and the vacuum pump 47 is actuated to evacuate thecontainer 70. The pressure in the atmosphere around the thin organicfilm material 74 in the container 70 is lowered, causing the thinorganic film material 74 to produce a vapor.

When the atmosphere of the container 70 is stabilized under apredetermined pressure, the on-off valve 45 is opened to permit thevapor of the thin organic film material 74 to flow from the container 70through the vapor outlet pipe 75 and the outlet port 44 into the vacuumchamber.

The vapor outlet pipe 75 is surrounded by a microheater 72 forcontrolling the temperature of the vapor outlet pipe 75 independently ofthe temperature of the heating medium 61. For emitting a vapor from thethin organic film material 74, the microheater 72 is energized inadvance to heat the vapor outlet pipe 75 to a temperature higher thanthe temperature of the thin organic film material 74.

Since the vapor outlet pipe 75 has been heated, the vapor of the thinorganic film material 74 is not cooled when the thin organic filmmaterial 74 flows through the vapor outlet pipe 75. Therefore, the thinorganic film material 74 will not be deposited in the vapor outlet pipe75, and the on-off valve 45 is prevented from being clogged.

After the interior of the vacuum chamber is stabilized under a pressureof 1.33×10⁻⁴ Pa (1.0×10 Torr), the same as the case of evaporationapparatus 10 in FIG. 1 an evaporation, source shutter positioned abovethe outlet port 44 is opened, and a stable discharge of the vapor of thethin organic film material 74 is confirmed by a film thickness monitorpositioned above the outlet port 44. Thereafter, a substrate shutter isopened to start depositing a thin organic film on the surface of a glasssubstrate.

After a thin organic film is deposited to a desired thickness, theon-off valve 45 is closed, blocking the vapor of the thin organic filmmaterial 74 against ingress into the vacuum chamber. The inactive gas isintroduced into the container 70, and the cooler 64 is actuated to lowerthe temperature of the heating medium 63. Since the inactive gas isintroduced into the container 70, increasing the pressure in thecontainer 70, the emission of a vapor from the thin organic filmmaterial 74 is prevented, and hence the thin organic film material 74 iscooled without being evaporated.

After the thin organic film is deposited on the surface of the glasssubstrate, the glass substrate is replaced with a next glass substrate,which will start being processed for the deposition of a thin organicfilm thereon in the same manner as described above.

The formation of a single-layer thin organic film on an object has beendescribed above with respect to the organic material evaporation source42 shown in FIG. 3. However, a plurality of organic material evaporationsources for forming a multiple-layer thin organic film on an object maybe employed such that a thin organic film material contained in each ofthe organic material evaporation sources is placed in an inactive gasatmosphere when the temperature thereof is increased and reduced.

The thin organic film material may be in the form of a solid or aliquid. If the thin organic film material is powdery, then since aninactive gas enters between particles of the powdery thin organic filmmaterial and acts as a heating medium, the rate at which the temperatureof the thin organic film material is increased and reduced is increased,increasing the ability of the thin organic film material to be uniformlyheated.

If the thin organic film material is in the form of a liquid, then sincethe temperature thereof is increased and reduced by the heating medium,the efficiency of a heat exchange is high. When the temperature of thethin organic film material is increased, as the temperature of thinorganic film material is not higher than that of a heating medium, thethin organic film material will not be subject to bumping. The heatingmedium may be a gas as well as a liquid such as silicone oil.

While a nitrogen gas has been employed as the inactive gas in the aboveembodiments, another gas may be employed insofar as it does not reactwith thin organic film materials.

According to the present invention, as described above, a thin organicfilm material does not emit a vapor when its temperature is increasedand reduced, and the rate at which the temperature of the thin organicfilm material is increased and reduced is increased.

Since temperature controllability of the thin organic film material isimproved to prevent a temperature overshooting, the thin organic filmmaterial is prevented from bumping.

Furthermore, because the ability of the thin organic film material to beuniformly heated is increased, the rate at which a vapor of the thinorganic film material is produced is stabilized within a short period oftime.

Although certain preferred embodiments of the present invention havebeen shown and described in detail, it should be understood that variouschanges and modifications may be made therein without departing from thescope of the appended claims.

What is claimed is:
 1. A vacuum evaporation apparatus having: a vacuumchamber; an organic material evaporation source holding an organic filmmaterial therein; an evacuating system for evacuating said vacuumchamber; wherein said vacuum evaporation apparatus to form an organicfilm on an object placed in said vacuum chamber by emitting a vapor fromsaid organic film material further comprising: a temperature controllerof an organic material for controlling said organic film material at avacuum evaporating temperature under the vacuum atmosphere; and apressure controller of vacuum atmosphere for controlling pressure of avacuum atmosphere around said organic film material to start and to stopemission of said vapor from said organic film material in said vacuumchamber.
 2. A vacuum evaporation apparatus according to claim 1, whereinsaid pressure controller controls pressure of a vacuum atmosphere byintroducing inactive gas into vacuum atmosphere around said organic filmmaterial.
 3. A vacuum evaporation apparatus according to claim 1,wherein said temperature control means is able to heat and cool saidorganic film material.